Integrated circuits are manufactured from wafers that are typically created by growing an elongated cylinder or boule of single crystal silicon and slicing individual wafers from the cylinder. Slicing may cause one or both faces of the wafer to be somewhat rough; however, at least one face of the wafer should be substantially flat in order to facilitate reliable semiconductor junctions formed from subsequent layers of material that may be applied thereto. Thus, chemical-mechanical polishing (CMP) is performed on each wafer to remove projections and other imperfections to create a smooth planar surface. After the wafer surface is planarized, various materials, such as metals, may be deposited over the wafer to create composite thin film layers. In some cases, the metals are initially over-deposited onto the wafer to form a relatively thick metal layer and a CMP process is employed to polish and thin the metal layer.
Generally, a CMP process thins the wafer and removes the projections and imperfections on the wafer by contacting the wafer with a polishing surface and an abrasive slurry. Relative motion between the wafer and polishing surface is provided at a selected rate, which may be controlled to yield a metal layer having a desired thickness.
To determine the thickness of the metal layer, some CMP tool configurations include an eddy current probe. The eddy current probe generates a magnetic field which experiences a magnetic flux change when a conductive material, such as, for example, the metal layer on the wafer, is passed therethrough. The magnetic flux change provides an impedance that is then used to extrapolate measurements of certain properties of a wafer, such as the hardness or density of the wafer or the thickness of the metal layer.
Although the above-mentioned method is generally effective in most circumstances, it may have drawbacks in other circumstances. For example, the CMP tool may become contaminated or its components may become worn over time. Consequently, the eddy current probe may obtain inaccurate impedance measurements. Specifically, in some instances a foreign metallic object may become trapped in or come into the vicinity of the magnetic field. Thus, the foreign metallic object may undesirably interfere with the magnetic field and may inadvertently adjust the impedance measurement so that the measurement may not be as accurate as desired. In another example, the polishing surface may be a pad that has a thickness that diminishes over use and time. Hence, the pad used to polish a first wafer may not have the same thickness when used to polish a second wafer, which may also affect the ability of the eddy current probe to obtain accurate impedance measurements.
Accordingly, it is desirable to have a CMP tool that is capable of calibrating its tool parameters to account for contamination and/or worn components. In addition, it is desirable for the tool to yield accurate impedance measurements, despite the presence of a contamination and/or worn component. Moreover, it is desirable for the tool to produce high quality wafers. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.